Windows Phone 7 will lock your upgrade SD card

AT&T is warning people not to replace the microSD cards in their Samsung Windows Phone 7 handsets because it could cause “performance degradation” or “device instability.” At least not yet.

Though Microsoft has said from the beginning that its Windows Phones wouldn’t support traditional SD card use, manufacturers such as Samsung put the cards in their phones anyway. That way everyone can say Windows Phone 7 devices have expandable memory.

This is true, but SD cards with Windows Phones don’t work the way they do with other devices. Windows Phone 7 reformats the cards to a specific format and combines the extra memory with the handset’s internal storage. That makes it difficult for a computer to read the card, and makes upgrading a phone’s storage risky.

“You should not remove the SD card in your phone or replace it with a new one because your Windows Phone won’t work properly,” Microsoft says on its website. “Existing data on the phone may be lost, and that SD card can’t be used in other devices or Windows Phones. “

It’s possible to buy a larger SD card to expand a Windows Phone’s storage, but AT&T is warning against it. That’s because Windows Phone 7 requires special SD cards that are compatible with the system — and no such cards are available yet in retail.

AT&T is telling people to “delay purchasing an external microSD card until the cards identified as ‘Certified for Windows Phone 7′ are available commercially or in AT&T stores.” If an unauthorized card is used, people could experience “performance degradation” or “device instability,” the wireless carrier said.

Microsoft did not immediately respond to a seattlepi.com request for comment.

Updated 4:20 p.m.: Here’s a statement from Microsoft:

Windows Phone 7 does not support swapping microSD cards in and out. SD cards inserted into a Windows Phone 7 device are integrated into the device’s file system and are intended to be a permanent modification to the device. Once an SD card has been integrated into a Windows Phone 7 device’s file system, it will no longer be readable or writable on any other device. This behavior is by design and is intended to ensure a consistently high-quality and secure end-user experience.

And here’s another statement from AT&T:

Windows Phone 7 requires a certified high-speed microSD card for optimal performance. Because the Samsung Focus is expandable via a microSD card, only microSD memory cards certified for Windows Phone 7 should be used. This information is not currently marked on any microSD packaging in market today. As a result, we are advising customers to delay purchasing an external microSD card until the cards identified as “Certified for Windows Phone 7″ are available commercially or in AT&T stores.